Heavy oils are generally referred to those hydrocarbon comprising oils with high viscosity or API gravity less than about 20. Crude oils and crude oil residuum obtained after atmospheric or vacuum distillation of crude oils that exhibit an API gravity less than about 20 are examples of heavy oils. Upgrading of heavy oils is important in production, transportation and refining operations. An upgraded heavy oil typically will have a higher API gravity and lower viscosity compared to the heavy oil that is not subjected to upgrading. Lower viscosity will enable easier transportation of the oil. A commonly practiced method for heavy oil upgrading is thermal treatment of heavy oil. Thermal treatment includes processes such as visbreaking and hydro-visbreaking (visbreaking with hydrogen addition). The prior art in the area of thermal treatment or additive enhanced visbreaking of hydrocarbons teach methods for improving the quality, or reducing the viscosity, of crude oils, crude oil distillates or residuum by several different methods. For example, the use of additives such as the use of free radical initiators is taught in U.S. Pat. No. 4,298,455; the use of thiol compounds and aromatic hydrogen donors is taught in EP 175511; the use of free radical acceptors is taught in U.S. Pat. No. 3,707,459; and the use of a hydrogen donor solvent is taught in U.S. Pat. No. 4,592,830. Other art teaches the use of specific catalysts, such as low acidity zeolite catalysts (U.S. Pat. No. 4,411,770) and molybdenum catalysts, ammonium sulfide and water (U.S. Pat. No. 4,659,543). Other references teach upgrading of petroleum resids and heavy oils (Murray R. Gray, Marcel Dekker, 1994, pp. 239-243) and thermal decomposition of naphthenic acids (U.S. Pat. No. 5,820,750).
Generally, the process of thermal treatment of heavy oil can result in an upgraded oil with higher API. In some instances, the sulfur and naphthenic acid content can also be reduced. However, the main drawback of thermal treatment of heavy oils is that with increased conversion there is the formation of toluene insoluble (TI) material. These toluene insoluble materials comprise organic and organo-metallic materials derived from certain components of the heavy oil during the thermal process. Generally, the TI materials tend to increase exponentially after a threshold conversion. Thus, the formation of TI materials limits the effectiveness of thermal upgrading of heavy oils. Presence of TI material in upgrading oils is undesirable because such TI materials can cause fouling of storage, transportation and processing equipment. In addition, the TI materials can also induce incompatibility when blended with other crude oils. Increasing conversion without generating toluene insoluble material is a long-standing need in the area of thermal upgrading of heavy oils. The instant invention addresses this need. As used herein, crude oil residuum or resid refers to residual crude oil obtained from atmospheric or vacuum distillation of a crude oil.